1. Field of the Invention
The present invention relates to a nuclear spin control device adapted to perform quantum-mechanic computing by controlling the spin of nucleus.
2. Description of the Related Art
Such a nuclear spin control device is utilized in a spin memory device, spin interference device, semiconductor polarizer and the like.
It is known that nuclear spin does not substantially interact with its surroundings environment and maintains a quantum mechanical state for a relatively long time. Thus, there is proposed quantum-mechanic computing by utilizing the above-mentioned property of nuclear spin to perform calculation in a relatively short time, which requires a considerably long time with existing digital computers. See, for example, B. E. Kane, xe2x80x9cNATURExe2x80x9d, 393, 133 (1998).
However, there exist difficulties in setting the initial state with all the nuclear spins aligned in the same direction, and controlling the interaction between the nuclear spins during the operation of the device, and such difficulties are considered to be the bottleneck in realizing quantum-mechanical computing with the nuclear spin.
It is an object of the present invention to provide the nuclear spin control device capable of setting the initial state with all the nuclear spins aligned in the same direction easily.
It is another object of the present invention to provide the nuclear spin control device capable of controlling the interaction between the nuclear spins easily.
According to one aspect of the present invention, there is provided a nuclear spin control device comprising:
a first semiconducting layer with spin-up carriers;
a second semiconducting layer with spin-down carriers; and
a third semiconducting layer arranged between the first and the second semiconducting layers, and capable of being tunnelled selectively by the spin-up carriers and the spin-down carriers such that nuclear spin in the third semiconducting layer selectively interacts with the spin-up carriers and the spin-down carriers so as to be oriented into a desired direction.
With the above-mentioned element according to the invention, the third semiconducting layer can be tunnelled selectively by the spin-up carriers and the spin-down carriers such that nuclear spin in the third semiconducting layer selectively interacts with the spin-up carriers and the spin-down carriers so as to be oriented into a desired direction. As a result of this, it is possible to set the initial state with all the nuclear spins aligned in the same direction easily. In the description, the desired spin direction of carriers means not only xe2x80x9cupxe2x80x9d and xe2x80x9cdownxe2x80x9d but also arbitrary desired direction which is realized by linear combination of both up and down states.
According to another aspect of the present invention, there is provided a nuclear spin control device comprising:
a first semiconducting layer with spin-up carriers;
a second semiconducting layer with spin-down carriers; and
a third semiconducting layer arranged between the first and the second semiconducting layers, and capable of being tunnelled selectively by the spin-up carriers and the spin-down carriers;
the nuclear spin control device being adapted to control the shape of a wave function so as to cover nuclear spins in the third semiconducting layer and propagate information of one nuclear spin to another nuclear spin.
With the above-mentioned element according to the invention, the nuclear spin control device being adapted to control the shape of a wave function so as to cover nuclear spins in the third semiconducting layer and propagate information of one nuclear spin to another nuclear spin. Thereby, it is possible to control the interaction between nuclear spins easily.
The nuclear spin control device may further comprise means for applying at least one of an electric field and a magnetic field to the device so as to control the shape of the wave function of at least one of the spin-up carriers and the spin-down carriers, as well as the spin-direction of carriers in each of the first and second semiconducting layers. As a result of this, the good adjustment of the direction of the nuclear spin can be achieved.
According to another aspect of the present invention, there is provided a method of controlling a nuclear spin in a nuclear spin control device, the device comprising a first semiconducting layer, a second semiconducting layer; and a third semiconducting layer arranged between the first and the second semiconducting layers, and capable of being tunnelled selectively by spin-up carriers and spin-down carriers;
the method comprising steps of:
adjusting a carrier concentration of the first and the second semiconducting layers such that the first semiconduting layer contains the spin-up carriers and the second semiconducting layer contains the spin-down carriers under proper electric and magnetic fields; and
interacting the nuclear spin in the third semiconducting layer selectively with the spin-up carriers and the spin-down carriers so as to be oriented into a desired direction.
With the above-mentioned method according to the invention, it is possible to set the initial state with all the nuclear spins aligned in the same direction easily.
Preferably, the spin direction of the carrier is adjusted by applying at least one of an electric field and a magnetic field, so that the good adjustment of the direction of the nuclear spin can be achieved.
According to another aspect of the present invention, there is provided a method of controlling a nuclear spin in a nuclear spin control device, the device comprising a first semiconducting layer, a second semiconducting layer; and a third semiconducting layer arranged between the first and the second semiconducting layers, and capable of being tunnelled selectively by spin-up carriers and spin-down carriers;
the method comprising steps of:
adjusting a carrier concentration of the first and the second semiconducting layers such that the first semiconduting layer contains the spin-up carriers and the second semiconducting layer contains the spin-down carriers under proper electric and magnetic fields; and
controlling a shape of a wave function so as to cover nuclear spins in the third semiconducting layer and propagate information of one nuclear spin to another nuclear spin.
With the above-mentioned method according to the invention, it is possible to control the interaction between nuclear spins easily.
Preferably, the spin direction of the carrier is adjusted by applying at least one of an electric field and a magnetic field. More preferably, the shape of the wave function is controlled by applying at least one of an electric field and a magnetic field. Thereby, the good control of the interaction between the nuclear spins can be achieved.